The heart rate monitor data above was recorded on 5/19/96 during the New Territory Triathlon. The distances were 1km swim / 30km bike / 5km run. A feature of the race was the bike course which was a straight, flat out and back, with a strong wind -- a tailwind going out, headwind coming home. Note that the heart rate data is reasonably flat during the bike leg. This is despite speeds of 28 mph with the wind, and 20 mph against the wind. A consistant physiological "power output" (ie. staying at a constant % of VO2 max) helps to give an even pace and to prevent "bonking".

As a side note, compare the average heart rate of this race to the average heart rate data from the Ironman races(Ironman Canada, or Ironman Europe) (same individual). The shorter race has a much higher average heart rate reflecting a higher % of VO2 maximum. This higher output would, of course, be unsustainable for an Ironman distance race.